Method and device for strengthening a non-woven material

ABSTRACT

Method for strengthening a web like fleece of fibrons material by applying a pattern of dots of a stiffening agent upon the fleece by means of one or more cylindrical stencils rotating in the direction of advance of the fleece.

United States Patent [191 Anselrode METHOD AND DEVICE FOR STRENGTHENING A NON-WOVEN MATERIAL [75] Inventor: Lodewijk Anselrode, St. Anthonis,

Netherlands [73] Assignee: Stork-Amsterdam N.V.,

Amstelveen, Netherlands [22] Filed: Oct. 29, 1970 [21] Appl. No.: 84,980

[30] Foreign Application Priority Data Oct. 30, 1969 Netherlands 6916397 [52] U.S. C1 ..1l7/38, 117/7, 117/119.8,

[51] Int. Cl B44d 3/18, B44d 1/48 [58] Field of Search 117/38, 7, 119.8;

[56] References Cited UNITED STATES PATENTS 2,698,574 1/1955 Dougherty et a1.... 117/38 Primary ExaminerA1fred L. Leavitt Assistant Examiner-M. F. Esposito AttorneyEdmund M. Jaskiewicz 57] ABSTRACT Method for strengthening a web like fleece of fibrons material by applying a pattern of dots of a stiffening agent upon the fleece by means of one or more cylindrical stencils rotating in the direction of advance of the fleece.

4 Claims, 2 Drawing Figures METHOD AND DEVICE FOR STRENGTHENING A NON-WOVEN MATERIAL SURVEY OF THE PRIOR ART The invention relates to a method for strengthening a weblike fleece of fibrous material, such as nonwoven material, by applying continuously a paste or emulsion containing a stiffening agent to the advancing fleece.

Fibrous and non-woven materials can be manufactured by means of two essentially different methods, viz.:

according to the wet method which in principle corresponds to the way in which also paper is manufactured;

according to the dry method, whereby the fibres in one way or the other are combined in a dry way to thereby form a loose fleece.

The fibres may lie pell mell in a totally arbitrary way or be more or less directed in one direction, as e.g., is the case with a carded fleece, in which the fibres are substantially lengthwise directed.

With the two methods it is necessary to strengthen the material by using so-called stiffening agents such as pastes, emulsions or solutions like rubber lattices, acrylate emulsions or solutions of e.g. synthetic rubbers etc. which cause the fleece composing fibres to adhere better to each other.

According to the various methods known in the art the fleeces are in one way or the other impregnated with an emulsion or solution of the stiffening agent, either by spraying, submerging, or rolling etc., whereupon the excess is removed by pressing or exhausting.

This known method has the considerable drawback that the applied quantity of stiffening agent is quite arbitrarily distributed on the entire material, while a microscopic examination tells that in a more economical way the application of the stiffening agent could be limited to the so-called junctions, that is to say the locations whereat two or more fibres contact or are in the close proximity of each other. In connection with the field of application of the non-woven materials it is of great importance to take this aspect into account.

SUMMARY OF THE INVENTION The invention aims at providing a new method for applying the stiffening agent and also a method of finishing, including drying the fleece treated in this way, thereby avoiding the aforementioned difficulties. The invention will further render it possible to influence the distribution and the density of the stiffening agent applied to the fleece in a manner which can be positively controlled, such that it is no longer required to remove an excess quantity of stiffening agent.

For that purpose the invention provides a method according to which the stiffening agent is applied by means of one or more thin-walled cylindrical screen stencils with squeegee, said stencils rotating in the direction of advance of the fleece.

An important advantage of the application of the screen stencils resides in the fact that the stiffening agent can be applied to the fleece according toa pattern; the agent can be printed" as it was into this pattern. It is further possible to control in a very positive way the quantity of stiffening agent, applied on the fleece per unit of surface, by means of the mesh width of the screen stencil and the pressing force of the squeegee. It is possible to print in a simple way the fleece to be strengthened according to a pattern of closed and perforated parts provided on the screen stencils.

By printing the fleece according to a particular pattern the fact can be taken into account that particular fleeces by nature exhibit already a strength greater in the longitudinal direction than in the transverse direction and in addition thereto it is possible to take the average fibre length of the fibres in the fleece into account. On a screen stencil the open parts could form a network of fine lines, in which the ones extending in a transverse direction with respect to the fleece web, are broader or closer to each other than the lines which are longitudinally directed. A great advantage of the invention is therefore that screen stencils are available which can be easily interchanged and upon which the desired pattern -adapted to the fleece to be strengthened can be easily provided. Further-more a large number of stencils can be kept in stock.

The fleece is preferably moved vertically downwards during and after application of the stiffening agent and the fleece is for a short time, after the liquid has been applied, not supported, so that due to its own weight a pull is exerted thereon. This method is advantageous in that the stiffening agent with which the fleece is printed according to a particular pattern has the time to penetrate into the fleece from the surface therof, while the pull gives rise to the formation of new junctions between the fibres gliding along each other. The junctions operate as capillaries which, if they contact the stiffening agent, tend to suck up same. Due to this capillary suction force a temporary enormous strengthening of the fleece is obtained, whereby on this fleece a particular pull can be exerted greater than on the dry nonstrengthened fleece. Since the stiffening agent applied to the surface is fast passed on to the inner capillaries, the fleece remains over a particular distance in a state of increased strength, only the area of the greatest strength is inwards displaced. The time during which this process continues can be regulated within particular limits by the quantity of stiffening agent which is applied.

Preferably the fleece is advanced from between two screen stencils rotating in opposite directions. This is advantageous in that the fleeces are thus printed on both sides with a pattern. If desired the pattern on either side of the fleece may be different whereby special effects can be obtained.

Preferably the fleece after having been moistened or printed with the stiffening agent is downwards moved in a vertical drying tunnel in which the fleece is at first not supported. This causes a positive pull to be exerted on the fleece leaving the screen stencils i.e., a pull obtained by the weight of the fleece itself. A drying tunnel comprising slits or perforations through which heated air can be blown in such a way on the two sides of the moistened fleece that same can be fast dried or heated without flapping or fluttering, is known per se. It is preferably arranged as described in the US. Pat. Specification 3 ,181 ,250. The special effect of the application of a vertical drying tunnel in combination with the present method consists in that the reorientation of the junctions between the fibres obtained due to the aforementioned pull can be regulated and varied as a result of a correct adjustment of the vertical current of air in the drying tunnel in relation to the total real weight of the web in the drying tunnel. As a result an adjustable apparent weight of the web is obtained which ensures the reorientation. This reorientation results necessarily in a natural equilibrium, since due to the reorientation the material becomes stronger. For the rest the forced vertically directed current of air can and will be directed up or down, so that the web becomes apparently lighter or heavier, respectively.

It should be noted that the conception underlying the invention is based on the understanding that ifa fibrous fleece, like a non-woven web-shaped material, is printed with a stiffening liquid according to a fixed pattern this can be effected in a regular way without it being necessary to discharge any excess liquid. The available junctions which have a capillarly effect suck up the stiffening agent. The advantage of the application of a screen stencil is in that the pattern printed on the fleece can be entirely tuned to the structure and dimensions of the fibres. So the existing junctions in the fleece are provided with the stiffening agent in a manner which is determined beforehand with easily variable means.

The further developed idea underlying the invention consists in that in order to accelerate the process of penetration, which is required to impregnate the fleece also internally with the stiffening agent, now junctions are formed. This formation is obtained by exerting a tensile force on the fleece which now due to a first strengthening can stand a pull. The new junctions are formed by (shifting) the fibres on each other so that an additional capillarly effect is created. Consequently the new junctions in the interior of the fleece are provided with stiffening agent and anchored with respect to each other.

The invention relates also to a device for strengthening a web shaped fleece of fibrous material comprising means for applying a paste or emulsion with a stiffening agent. As already mentioned, on using the conventional known rollers for applying a stiffening agent, the drawback of excess liquid arises.

It is an object of the invention to provide a device ca pable of printing a pattern of a stiffening agent on the fleece in a positively to be regulated manner. For that purpose the invention provides a device wherein the means for applying the agent consist of one or more rotatable thin-walled cylindrical screen stencils with inner squeegee, means being provided to move the fleece past or from between the said stencils.

It has been found that the above described method can be extended in order to obtain a fibre fleece provided with a thermoplastic glue layer that is to say a fleece which can be used as an adhesive intermediate lining.

The improvement to that effect of the aforementioned method consists in that one composes the paste such that it does not completely gel when being dried or moderately warmed.

Due to this feature it is not necessary to start from an already existing and strengthened non-woven product, but it becomes possible to obtain an adhesive fibre fleece by starting from a fleece which is not strengthened by binder chemicals e.g., from a fleece which comes directly from e.g., a carding machine.

By means of a screen cylinder a discontinuous pattern of chemicals is provided in this non-strengthened fleece in such a way that after drying or heating not only a sufficient strengthening of the fleece is obtained but moreover a sufficient quantity of binding agent is present in the fibres situated on the surface of the fleece on at least one side thereof, while this agent has the property that in contact with a second material and under a moderate pressure it adheres thereto.

On performing the method according to the invention there is a risk of the fibres of the fleece adhering to the stencil. This is caused by the outflow of the paste in the direction of advance of the fibre fleece. These difficulties are obviated when according to the invention the fleece in the contact area with the stencil(s) is supported according to a curved surface the curvature of which is the mirror image of the curvature of the concerning stencil.

The invention will be clarified with reference to the accompanying drawing in which two variants of a device for performing the method is diagrammatically represented.

DESCRlPTlON OF PREFERRED EMBODIMENTS As shown in FlG. l a converyor belt 1 advances a web-shaped fleece of non-woven material 2, as far as between two screen cylinders 3 and 4 each provided with a squeegee 5. The material is there printed in the proper way according to the pattern in the surface of the two screen stencils 3, 4. Immediately the capillaries in the proximity of the surface of the web will be saturated. Due to this capillary suction force a temporary (enormous) strengthening of the fleece is obtained, whereby a certain pull can be exerted on this fleece. The fleece 2 remains over a particular distance in a condition of increased strength, so that a tensile force corresponding to the own weight of the fleece can be applied thereto.

The fleece 2 is thereupon moved downwards in a drying tunnel 6 where through means 7 are dried or heated. The pull required for the reorientation of the junctions can be obtained by the precise adjustment of the vertical current of air present in the drying tunnel. Prior to a possible fracture of the fleece due to a decrease of its wet strength, the fleece is fast dried from the outer side, in the upper part of the drying tunnel, thereby increasing its strength rapidly. While the drying process starts already on the outer side and a strengthening is produced the last part of the penetration process takes place within the fleece.

it should be pointed out that it is further possible to carry out chemical reactions in the lower part 8 of the drying tunnel e.g. a polymerisation reaction by means of a raise of termperature. Also additional components can be introduced into the system e.g., in the shape of gas or a cloud.

FIG. 2 shows a variant in which a non-strengthened fleece 2 is laid on a smooth conveyor belt 1 guided by sprocket wheels 9. A screen cylinder 11 provided with a squeegee mechanism 12, supported by a counterpressure and turning wheel 10, presses the chemicals required for strengthening purposes on and into the fleece web. Good results can be obtained with a polyvinylchloride plastisol according to the following composition:

100 parts of a co-polymer of parts of polyvinylchloride and ten parts of polyvinylacetate,

parts of a polymer plasticiser on a base of phthalic acid,

one part of a thixotropic thickener on a base of castor oil,

1 1/2 part of a zinc-calcium stabiliser,

two parts of epoxydated soja bean oil,

parts of turpentine, boiling range 159200C.

This printing mass is applied as a pattern of lines intersecting at right angles with intermediate non-printed squares having sides of 3 mm. Starting from a nonstrengthened card fleece consisting of rayon fibres of 3.7 denier and a length of fibre of 60 mm and increase in weight of 1 l0 grams per m was obtained.

The fleece web printed in this way is introduced into a drying chamber 13 and dried at a temperature of 115C at which temperature the turpentine is evaporated and a pre-gelling of the polyvinylchloride is taking place. When a web of the product obtained in this way is laid with its printed face upon a web of cotton fabric and is pressed for thirty seconds in a press at a temperature of 150C and a press pressure of 300 grams per cm then a very good adherence of the two materials is obtained.

When two webs of the product obtained are laid against one the other by their non-printed sides and subsequently are laid between two cotton fabric webs and are pressed on one the other under the aforementioned conditions, then it appears that not only a sufficient adherence of the two non-woven webs on the cotton webs is obtained, but also at least as good an adherence between the non-woven webs mutually.

The invention is not limited to the use of polyvinylchloride plastisols. Corresponding products can be obtained with:

nylon-suspensions and nylon-solutions or suspensions and solutions, respectively of polyethylene, so-called heatsealable acrylate lattices etc.

What I claim is:

1. A method for strengthening a web-shaped fleece of non-woven fibrous material, comprising the steps of applying continuously a paste or emulsion containing a stiffening agent to the advancing fleece as a printed pattern by means of one or more thin-walled, cylindrical, screen stencils with squeegee while rotating the stencils in the direction of advance of the fleece, continuously moving the fleece vertically downwards during and after application of the stiffening agent, the fleece is for a short time, after the stiffening agent has been applied, not supported, so that due solely to its own weight a pull is exerted thereon, and thereafter moving the treated unsupported fleece downwards through a drying chamber while unsupported to produce a dried strengthened web of fleece.

2. A method according to claim 1, in which the fleece is moved from between two stencils which are rotating in opposite directions.

3. A method according to claim 1, in which the fleece after having been moistened or printed with the stiffening agent is downwardly moved in a vertical drying tunnel in which the fleece is at first not supported.

4. A method according to claim 3, in which the weight of the web of the printed part of the fleece is regulated by a forced vertically directed current of air. 

2. A method according to claim 1, in which the fleece is moved from between two stencils which are rotating in opposite directions.
 3. A method according to claim 1, in which the fleece after having been moistened or ''''printed'''' with the stiffening agent is downwardly moved in a vertical drying tunnel in which the fleece is at first not supported.
 4. A method according to claim 3, in which the weight of the web of the printed part of the fleece is regulated by a forced vertically directed current of air. 